Modern asphalt roofing shingles generally are formed from asphalt saturated and coated fibrous webs covered on an upper side with protective ceramic granules. Each shingle includes an upper headlap portion and a lower portion that is exposed on a roof. The headlap portion is designed to be overlapped by the lower portions of a next higher course of shingles when the shingles are installed. The lower portion often is separated by slots into individual tabs of the shingle, which are exposed on a roof after installation. Other shingle configurations also exist. For example, higher end roofing shingles may comprise two laminated plies of shingle material adhered together with at least the top ply being cut into tabs commonly known as “dragon teeth” to lend texture and the appearance of thickness to a shingle installation.
Regardless of the style of asphalt shingle, raising and consequent tearing of exposed shingle tabs during high wind conditions often results in rainwater leakage and ultimate failure of a shingle system. It therefore is highly desirable and even necessary that the exposed portions of asphalt shingles be adhered to the headlap portion of underlying shingles to minimize the rising of the exposed portions caused by high winds. This is commonly accomplished by the application of a sealant strip to the headlap portions of shingles just above the lower exposed portions. These sealant strips soften when shingles are heated by the sun to bond the overlapping portions of one course of shingles to the head lap portions of shingles in a next lower course. Such strips, often referred to as “self-seal strips” usually are applied in a discontinuous line defined by short dashes of sealant separated by short spaces that contain no sealant. The spaces are important because they allow moisture that may penetrate or condense above the self-seal strip to drain through the spaces between the bonded dashes of the strip. Discontinuous strips also reduce the amount of sealant needed.
In the past, self-seal strips have been applied during the manufacturing process by passing a web of shingle stock over a rotating self-seal applicator wheel that contacts or passes closely adjacent the shingle stock to apply the sealant. The applicator wheel has a peripheral surface that in one embodiment is defined by a plurality of lands separated by gaps. In operation, the wheel is rotated with a surface speed that is substantially the same as the line speed at which shingle stock is moving. The wheel passes through an underlying sump carrying liquid sealant and, in turn, picks up sealant on its lands and in the gaps between the lands. The loaded lands then rotate upwardly to contact the moving web of shingle stock and the sealant on the lands is transferred to the shingle stock. Because the lands are spaced apart by gaps, this produces intermittent dashes of sealant separated by spaces extending along the shingle stock, which together define the self-seal strip.
While the above technique for applying a self-seal strip produces adequate results at common line speeds of up to about 850 feet per minute (fpm) used in the past, it has been found to be inadequate at higher line speeds. This is at least in part because at such higher speeds, the applicator wheel must be rotated at higher rates for its surface speed to match or approximate the line speed. Under these operating conditions, sealant that may have been captured within the gaps between lands tends to sling outwardly under the influence of centrifugal force as the applicator wheel rotates. This results in strings or ribbons of sealant that extend between the lands and that are slung outwardly from the gaps. These strings and ribbons ultimately are slung against and get applied to the shingle stock. This results in strings of sealant known as sealant bridges that extend between individual dashes of the self-seal strip. Bridges are undesirable, of course, because the self-seal strip now becomes essentially continuous and lacks the important spaces that allow rainwater or moisture drainage between the dashes of the sealant strip.
A need exists for a method and apparatus that can apply self-seal strips to moving shingle stock webs at higher line speeds without the stringing and bridging that results from prior art self-seal strip application techniques. It is to the provision of such a method and apparatus that the present invention is primarily directed.